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The investigation into the implementation and widespread adoption of oyster shell recycling methods aimed at restoring coastal ecosystems and enhancing water quality is currently limited. In this study, we investigated the utilization of oyster shell powder (OSP) as a cost-effective and environmentally sustainable method for treating high-fluoride-concentration wastewater, a byproduct of industrial processes. We conducted extensive laboratory testing to determine the optimal conditions for fluoride removal. This involved variations in OSP doses, particle sizes, and initial wastewater pH levels. The results of these tests showed that OSP achieved fluoride removal efficiencies exceeding 98% at an optimal dosage of 5 g/L. In addition, OSP effectively adjusted the wastewater pH from highly acidic (pH 2) to almost neutral (pH 6.87), demonstrating its effectiveness in real-world industrial wastewater treatment. OSP, derived from oyster shell waste, is rich in calcium carbonate and offers a novel approach to wastewater management by leveraging a natural waste product. This study demonstrates the potential of OSP as a waste management strategy and contributor to the circular economy by repurposing industrial byproducts.

In this study, spent coffee grounds (SCG) were treated using sodium hypochlorite (NaClO) to remove organics. The NaClO-treated SCG was modified with 3-aminopropyltriethoxysilane (APTES) to improve its adsorption performance. To understand the characteristics of the prepared adsorbents, samples were characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The pH edge, kinetic, and isotherm experiments were conducted to evaluate the adsorption performance of APTES-SCG for Reactive Black 5 (RB5), Reactive Orange 16 (RO16), and Reactive Yellow 2 (RY2). The pH edge experiments were carried out in the pH range of 2-12 at an initial dye concentration of 100 mg/L. The results showed that the dye uptakes on APTES-SCG increased with decreasing pH value. The adsorption experiments for kinetics confirmed that the equilibrium time was reached within 30 min at pH 2. The adsorption isotherm experiments were performed at initial dye concentrations of 30 to 300 mg/L, and the experimental data were well-fitted by the Langmuir model. The dye-loaded APTES-SCG was desorbed using 0.01 M NaOH solution and repeated adsorption-desorption experiments showed that APTES-SCG could be reused at least 3 times.

In this work, a new adsorbent with effective Pd(II) adsorption ability was synthesized using an oyster shell and fumed silica as the matrix materials and polyethyleneimine as the functional ligand. The adsorption performance of the developed adsorbent was evaluated for the recovery of palladium chloride ions (Pd(II)) from strong acid solutions. To understand the characteristics of the materials used in the study, samples were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD), and zeta potential analysis. Zeta potential analysis revealed that the isoelectric point of polyethylenimine-crosslinked calcium silicate hydrate (PEI-CSH) was 9.85. Isotherm experiments revealed that the maximum Pd(II) uptake estimated by the Langmuir model was 156.03 mg/g, which was 22.4 and 35.6 times higher than that of the oyster shell powder (OSP) and calcium silicate hydrate (CSH), respectively. The Pd(II) adsorption equilibrium was established in 180 minutes, according to kinetic experiments. These results suggested the possibility of Pd(II) recovery from oyster shell-based adsorbent. Through five adsorption and desorption cycles, the reusability of PEI-CSH was confirmed. PEI-CSH can therefore be considered a potential adsorbent for Pd(II) recovery.

In this study, an effective polyethylenimine-crosslinked PVC electrospinning nanofiber (PEI/PVC-NF) adsorbent was developed to remove Reactive Black 5 (RB5) from water. FT-IR and FE-SEM analysis showed that PEI/PVC-NF was prepared successfully, and the desorption process under strongly alkaline conditions had a negligible effect on the nanofiber structure. The adsorption performance of RB5 on PEI/PVC-NF was evaluated using pH edge, adsorption kinetics, and adsorption isotherm studies. The results were as follows: the pH edge experiment revealed that PEI/PVC-NF has a high adsorption capacity for RB5 from pH 2 to 8. Kinetic experimental results demonstrated that the pseudo-first-order and the pseudo-second-order kinetic models described the adsorption of PEI/PVC-NF to low and high concentrations of RB5. The adsorption process was exothermic in isotherm studies, and the Langmuir model suited the data better. At 25 °C, the Langmuir model indicated that RB5 had a maximum adsorption capacity of 1,017.06 mg/g. Five repeated regeneration experiments proved its good reusability. PEI/PVC-NF is a prospective adsorbent for reactive dye removal because of its high adsorption capacity, rapid adsorption kinetics, easy separation, and acid and base resistance.

In this study, a poly(acrylic acid)-modified polysulfone-Escherichia coli biomass composite fiber (PAA-PSBF) was used for the removal of Cd(II) from aqueous solution. FT-IR analysis confirmed that PAA was successfully modified on the PSBF surface. The adsorption and desorption properties of PAA-PSBF for Cd(II) were evaluated through pH edge, adsorption kinetic, adsorption isotherm, and desorption experiments. The pH edge experiments were carried out at initial Cd(II) concentrations of 50 and 100 mg/L, in the pH range of 2-7. The results showed that the optimal pH for Cd(II) removal was 7. The adsorption kinetic experiments confirmed that the adsorption equilibrium at pH 7 requires at least 240 min. The isotherm experimental data were well fitted by the Langmuir model, and the maximum Cd(II) uptake on PAA-PSBF was calculated as 47.39 mg/g. In addition, the reusability study revealed that the adsorption capacity of PAA-PSBF for Cd(II) was only slightly decreased while its desorption efficiency remained at above 93.88 %.

Heavy metals such as Pb(II) are toxic to ecosystems and humans, and removing heavy metals from water has always been a hot issue. Polyvinyl chloride (PVC) is a widely used synthetic polymer, however, the disposal of waste PVC is still challenging. In this study, polyethylenimine-crosslinked PVC fiber (PEI-PVCF) was developed to remove Pb(II) from aqueous solutions, which not only helps to remove heavy metals, but also provides a possible method for the recycling of waste PVC. The FTIR analysis verified that the PEI was successfully crosslinked with PVC. The effect of pH, contact time, and initial concentration on the adsorption of Pb(II) by PEI-PVCF were evaluated. Through the pH effect experiment, pH 6 was determined as the most suitable pH for Pb(II) removal from aqueous solutions. The isotherm experimental data was well explained by Langmuir model and the maximum Pb(II) uptake was evaluated to be 233.3 mg/g. Pseudo-second-order kinetic model well described the adsorption kinetic data of Pb(II) on PEI-PVCF. The adsorption equilibrium was reached within 120 min at all initial concentrations evaluated. Besides, intraparticle diffusion model proved multiple rate-limiting steps involved in Pb(II) adsorption process. As a result, PEI-PVCF can be considered as a promising adsorbent for Pb(II) removal due to its low cost, high adsorption capacity, and short adsorption equilibrium time.

This study reports a polyethylenimine-chitin composite biosorbent (PCCB) capable of high-efficiency recovery of Pd(II) from acidic solutions. To confirm that PCCB was successfully prepared, it was characterized by elemental analysis, FE-SEM, BET analysis, FT-IR, 13C solid-state NMR, and XPS. The PCCB exhibited a high adsorption capacity of 758.4 mg/g for Pd(II), and its adsorption equilibrium reached very quickly (within 10 min) in the initial Pd(II) solution of 50 to 200 mg/L. In addition, Pd(II) adsorption by PCCB maintained high adsorption capacities in the temperature range of 298 to 328 K and was not affected by interfering ions. Besides, mechanism studies revealed that the binding between PCCB and Pd(II) was mainly achieved by electrostatic interaction and reduction reaction. Even after 5 times of reuse, the adsorption and desorption efficiencies remained above 99%. Therefore, PCCB can be considered as a candidate adsorbent with a high potential for Pd(II) recovery from acid solutions.

In this study, a polysulfone Escherichia coil biomass composite fiber (PSBF) was prepared by thoroughly mixing and extruding a mixture of polysulfone and E. coil biomass. poly(acrylic acid) (PAA) was then crosslinked on the PSBF surface to fabricate PAA-PSBF. The adsorption performance of PAA-PSBF on Methylene Blue (MB) was evaluated by several batch tests such as pH edge, adsorption kinetics and adsorption isotherm. Desorption experiments were also conducted to examine the desorption efficiency and reusability of PAA-PSBF. As a result, it was optimal at pH 7 to remove MB by PAA-PSBF. The result of the kinetic experiments showed that at least 300 min was required to reach the adsorption equilibrium at the initial dye concentration of 200 mg/L. The isotherm experiment data were well illustrated by the Langmuir model and the maximum dye uptake was 225.2 mg/g at pH 7. By using a HCl-acidified solution with pH 2 as an eluent, the MB adsorbed on the PAA-PSBF was easily desorbed and the depleted PAA-PSBF was successfully regenerated. In addition, PAA-PSBF can be reused at least 3 times with good reusability.

Chitin is a natural polymer material that is abundant and easy to use at a low cost. In this research, a chitin-based adsorbent, polyethylenimine (PEI)-crosslinked chitin (PEI-chitin), was prepared by crosslinking PEI after binding glutaraldehyde to the specific functional groups of chitin surface. Its adsorption performance on Reactive Black 5 (RB5) was evaluated by batch and fixed-bed column studies. Regeneration study was also conducted to assess the reusability of PEI-chitin. The main results were as follows: pH 2 was optimal for the removal of RB5 from aqueous solution. Langmuir model was better fitted with the isotherm experimental data and the maximum adsorption capacity of RB5 was calculated to be 321.6 mg/g at pH 2. Pseudo-second-order model was better for depicting the kinetic data. The Thomas model can be well adapted to the breakthrough curves. The consecutive adsorption-desorption experiments were performed up to 3 cycles in batch and fixed-bed column systems. The sorption and desorption efficiencies in the batch system were at least 89.1 % and 92.2 %, while the column experiments showed 94.7 % and 97.6 %, indicating high potential in practical large-scale applications.

In this study, a poly(acrylic acid)-modified polysulfone-Escherichia coli biomass composite fiber (PAA-PSBF) was used for the removal of Cd(II) from aqueous solution. FT-IR analysis confirmed that PAA was successfully modified on the PSBF surface. The adsorption and desorption properties of PAA-PSBF for Cd(II) were evaluated through pH edge, adsorption kinetic, adsorption isotherm, and desorption experiments. The pH edge experiments were carried out at initial Cd(II) concentrations of 50 and 100 mg/L, in the pH range of 2-7. The results showed that the optimal pH for Cd(II) removal was 7. The adsorption kinetic experiments confirmed that the adsorption equilibrium at pH 7 requires at least 240 min. The isotherm experimental data were well fitted by the Langmuir model, and the maximum Cd(II) uptake on PAA-PSBF was calculated as 47.39 mg/g. In addition, the reusability study revealed that the adsorption capacity of PAA-PSBF for Cd(II) was only slightly decreased while its desorption efficiency remained at above 93.88 %. [ABSTRACT FROM AUTHOR]